The 20-year-old, who has made one senior appearance since his move from Wycombe in January last year, has signed a deal until 5 January.
"We knew about Kadeem from when he was at Wycombe and he has developed during his time at Cardiff," Brentford manager Uwe Rosler told the club website.
"He offers us something that I have been looking for since we lost Conor McAleny to injury."
The German added: "We need pace on the flanks. "He will give us pace, directness, dribbling ability and will terrorise defences.
"That is what we need to give us another option for our attacking game."
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